The present invention relates to a process for feeding oxygen-enriched air into a non-ferrous metal production unit comprising, on the one hand, a smelter for smelting an ore concentrate of the said metal, fed by continuously injecting oxygen-enriched air and, on the other hand, a converter for converting the matte coming from the smelter, fed by injecting oxygen-enriched air with a variable flow rate, and to a plant for implementing this process. The invention applies in particular to the production of copper.
The pressures mentioned below are absolute pressures.
Copper production units conventionally consist of a smelter operating continuously, such as a flash furnace, a Noranda furnace or a Teniente furnace, and of a converter operating batchwise, such as a Pierce converter or a Hoboken converter.
The raw material, composed of copper ore concentrate, is charged into the smelter, in which it becomes enriched with copper. A copper-rich mixture called xe2x80x9cmattexe2x80x9d, containing by weight approximately 60 to 70% copper, is then obtained. This matte is then further enriched with copper in the converter and is converted into what is called xe2x80x9cblisterxe2x80x9d copper containing approximately 99% copper.
In order for the smelting and the conversion to take place correctly, the smelter and the converter are fed with streams of oxygen-enriched air. The smelter consumes a constant stream of oxygen-enriched air. In contrast, the converter consumes a variable stream of oxygen-enriched air. Moreover, this stream may be close to zero when, the conversion into blister copper having been completed, the ladle of the converter is emptied in order to recover the blister copper and thus be able to start a new copper production cycle. Typically, a copper production cycle lasts approximately two hours, distributed as follows:
oxygen-enriched air is injected into the converter for approximately one hour;
the injection is stopped, the slag floating on the surface of the liquid copper is removed, the ladle is drained in order to recover the copper, after which the ladle is recharged with matte and a new cycle is started.
While the ladle is being drained, a gentle stream of oxygen-enriched air is maintained in order to maintain the flame of the converter burners. The degree of oxygen enrichment of the air depends on the composition of the raw material and on the expected production. As a general rule, the stream of air feeding the smelter is enriched with up to 28% oxygen and the stream of air feeding the converter is enriched with 50 to 60% oxygen.
Conventionally, the smelter and converter each have an air blower, the stream of air from which is enriched by injecting oxygen produced by a plant independent of the two air blowers.
Since the consumption of oxygen-enriched air by the smelter is constant, the air blower connected to the smelter permanently produces an air stream corresponding to the maximum flow rate of the copper production cycle. In contrast, since the consumption of oxygen-enriched air by the converter is variable, the difference between the output of air produced by the blower connected to the converter, which operates continuously, and that consumed by this converter is generally vented to atmosphere.
The oxygen production plant consists of an air compressor and an air separation unit which is capable of delivering a variable flow of oxygen so as to enrich the air stream of the blower for the smelter with a constant oxygen stream and to enrich the air stream for the converter with a variable oxygen stream.
The term xe2x80x9ccompressorxe2x80x9d is understood here to mean an actual compressor or several compressors mounted in parallel and having a common delivery.
This process for producing oxygen-enriched air by a plant comprising two independent air blowers connected to an oxygen production unit has various drawbacks, such as large overall size, considerable energy consumption and not insignificant loss of energy due to the air delivered by one of the blower being vented to atmosphere.
It is therefore an object of the invention to provide a process and a plant for feeding oxygen-enriched air into a non-ferrous metal production unit, which is smaller in overall size and which allows the energy expenditure to be substantially reduced.
The subject of the invention is therefore a process for feeding oxygen-enriched air into a non-ferrous metal production unit comprising, on the one hand, a smelter for smelting the concentrate of the said metal, fed by continuously injecting oxygen-enriched air and, on the other hand, a converter for converting the matte coming from the smelter, fed by injecting oxygen-enriched air with a variable flow rate, characterized in that:
all of the air is compressed in a single compressor capable of feeding the smelter and the converter;
some of this compressed air is treated in an air separation unit in order to obtain two oxygen streams which are injected into the compressed air intended for feeding the smelter and the converter, respectively; and
the compressed air or oxygen-enriched compressed air intended for the converter is stored in a buffer tank when the consumption of oxygen-enriched air by the converter is below a predetermined threshold and compressed air or oxygen-enriched compressed air is removed from the buffer tank when the consumption of oxygen-enriched air by the converter is above the said threshold.
According to other features of this process:
the smelter is fed by mixing air compressed by the first compression level of the compressor with oxygen produced by the air separation unit substantially at the same pressure;
the air separation unit is fed with compressed air by a compression level of the compressor located behind the first compression level of this compressor;
the converter is fed by mixing air compressed by the compressor to a pressure above the feed pressure of this converter with oxygen produced by the air separation unit substantially at the same pressure, by storing the oxygen-enriched air in the said buffer tank when the consumption of oxygen-enriched air by the converter is below the said threshold and by removing oxygen-enriched air from this buffer tank through an expansion device when the consumption of oxygen-enriched air by the converter is above the said threshold;
air compressed by the final stage of the compressor to a pressure above the feed pressure of the converter is stored in the said buffer tank when the consumption of oxygen-enriched air by this converter is below the said threshold and the converter is fed by mixing air stored in the buffer tank and/or air compressed by the final stage of the compressor, both air streams being removed through an expansion device, with oxygen produced by the air separation unit at a variable rate and at a pressure substantially equal to the feed pressure of the converter;
the air intended for the converter is compressed by the final stage of the compressor.
The subject of the invention is also a plant for implementing the process defined above. This plant is characterized in that it comprises:
an air separation unit designed to deliver oxygen to the smelter and the converter;
a single air compressor, the delivery side of which is connected to the smelter, to the air separation unit and to the converter via first, second and third lines respectively; and
a buffer tank connected to the said third line.
According to other features of this plant:
the buffer tank is also connected, on the one hand, to an oxygen output line from the separation unit intended for the converter and, on the other hand, to this converter via an expansion device. The buffer tank is also connected to the converter via an expansion device and an oxygen output line from the separation unit intended for the converter runs into the line which connects this expansion device to the converter.
the air separation unit comprises two oxygen production circuits, one feeding the smelter and the other feeding the converter;
the oxygen production circuit feeding the converter is provided with means for adjusting the oxygen flow rate;
the air separation unit is a double-column air distillation unit which includes a swing system so as to produce a variable stream of oxygen by distillation of a constant air input;
the air compressor comprises at least two compression levels, the delivery of the first level being connected to the said first line and the delivery of the following level or levels being connected to the said second and third lines;
the compressor has three compression levels, the deliveries of which are connected to the said first, second and third lines, respectively.
As will have been understood, the invention essentially consists in combining the air production with the oxygen production so that oxygen-enriched air for feeding the smelter and the converter of a non-ferrous metal production unit is produced more economically.